How to identify how XML output of ListBox would look like

Hello,

I am trying to build an APP, where there is a LIST BOX for the users to select some COLUMNS. I need to pass this information to a MACRO within the APP via an ACTION tool using "Update RAW XML with Formula".

Now my MACRO XML looks something like 

<Configuration>
<Value name="List Box (25)">COLA=False,COLB=False,COLC=False,COLC=False</Value>
</Configuration>

I need to udpdate this to 

<Value name="List Box (25)">COLA=True,COLB=True,COLC=False,COLC=False</Value>

if I am selecting COLA and COLB from LISTBOX.

To do this, I think I need to identify in which format LISTBOX returns values. Can some one throw some light into this ?

Thanks

Antony.